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xsk: Elide base_addr comparison in xp_unaligned_validate_desc

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Remove redundant (base_addr >= pool->addrs_cnt) comparison from the
conditional.

In particular, addr is computed as:

    addr = base_addr + offset

... where base_addr and offset are stored as 48-bit and 16-bit unsigned
integers, respectively. The above sum cannot overflow u64 since base_addr
has a maximum value of 0x0000ffffffffffff and offset has a maximum value
of 0xffff (implying a maximum sum of 0x000100000000fffe). Since overflow
is impossible, it follows that addr >= base_addr.

Now if (base_addr >= pool->addrs_cnt), then clearly:

    addr >= base_addr
         >= pool->addrs_cnt

Thus, (base_addr >= pool->addrs_cnt) implies (addr >= pool->addrs_cnt).
Subsequently, the former comparison is unnecessary in the conditional
since for any boolean expressions A and B, (A || B) && (A -> B) is
equivalent to B.

Signed-off-by: Kal Conley <kal.conley@dectris.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/bpf/20230411130025.19704-1-kal.conley@dectris.com
This commit is contained in:
Kal Conley 2023-04-11 15:00:25 +02:00 committed by Daniel Borkmann
parent 4099be372f
commit 1ba83f505c
1 changed files with 2 additions and 6 deletions
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8
net/xdp/xsk_queue.h
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@ -149,16 +149,12 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
struct xdp_desc *desc)
{
u64 addr, base_addr;
base_addr = xp_unaligned_extract_addr(desc->addr);
addr = xp_unaligned_add_offset_to_addr(desc->addr);
u64 addr = xp_unaligned_add_offset_to_addr(desc->addr);
if (desc->len > pool->chunk_size)
return false;
if (base_addr >= pool->addrs_cnt || addr >= pool->addrs_cnt ||
addr + desc->len > pool->addrs_cnt ||
if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt ||
xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
return false;